ML17229A115

Informs That Util Agrees W/Nrc Staff Re Importance of Issues Surrounding Revised LBLOCA Evaluation Model.Final Analysis of Impact of Model Error on ECCS Acceptance Criteria Will Be Prepared

ML17229A115
Person / Time
Site:	Saint Lucie
Issue date:	10/25/1996
From:	Bohlke W FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
L-96-283, NUDOCS 9611050179
Download: ML17229A115 (7)

Text

CATEGORY 1 REGULAT INFORMATION DISTRIBUTION STEM (RIDS)

ACCESS3;0$ . NBR:9611050179 DOC.DATE: 96/10/25 NOTARIZED: NO DOCKET FACIL:50-335 St. Lucie Plant, Unit 1, Florida Power 6 Light Co. 05000335 AUTH. NAME AUTHOR AFFILIATION BOHLKE,W.H. Florida Power a Light Co.

RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)

SUBJECT:

Informs that util agrees w/NRC staff re importance of issues surrounding revised LBLOCA evaluation model. Final analysis of impact of model error on ECCS acceptance criteria will be prepared. A DISTRIBUTION CODE: A001D COPIES RECEIVED:LTRK ENCL SIZE:

TITLE: OR Submittal: General Distribution E

NOTES:

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INTERNAL: ACRS 1 1 FILE CENTER 1 1 NRR/DE/EMCB 1 1 RR/DRCH HICB 1 1 NRR/DSSA/SPLB 1 1 NRR/DSSA/SRXB 1 1 NUDOCS-ABSTRACT 1 1 OGC/HDS3 1 0 EXTERNAL: NOAC 1 1 NRC PDR 1 1 D

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Florida Power & Light Company, P.O. Box 14000, Juno Beach, FL 33408-0420 OgT 2 5 1996 L-96-283 10 CFR 50.46 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Re: St. Lucie Unit 1 Docket No. 50-335 Revised LBLOCA Evaluation Model; Prelimina Assessment of Im act on PCT Ref: (1) NRC letter: Brian W. Sheron to T.F. Plunkett, 10 CFR 50.46 LARGE BREAK LOSS-OF-COOLANT ACCIDENT EVALUATIONMODEL FOR ST. LUCIE PLANT, UNIT 1 (TAC NO.

M96355); October 11, 1996.

(2) Telecon 10/24/96, 4:00 pm, J.A. Zwolinski(NRC), et al, to W.H. Bohlke (FPL), et.al.

Reference (1) informed Florida Power and Light Company (FPL) of problems identified by the NRC concerning changes to the Siemens Power Corporation (SPC) large break loss-of-coolant (LBLOCA) evaluation model used by SPC for pressurized water reactors. The letter requested that FPL evaluate, in accordance with 10 CFR 50.46(a)(3)(ii), the impact of identified model errors and changes, and take whatever actions are required to assure compliance with 10 CFR 50.46.

FPL agrees with the NRC staff regarding the importance of the issues surrounding the subject LBLOCAevaluation model. As discussed in Reference (2), FPL has agreed to document the current assessment and the rationale leading to FPL's conclusion that St. Lucie Unit 1 is operating in compliance with 10 CFR 50.46. The attachment to this letter contains that assessment with supporting rationale.

Because the current assessment's calculational results have not received final verification by SPC, FPL is also preparing a final analysis of the impact of the LBLOCAmodel error on emergency core cooling system acceptance criteria. FPL will submit this analysis to the NRC upon completion of its review of SPC revised calculational model final results.

Please contact us if there are any questions regarding this submittal.

Very truly yours, W. H. Bohlke Vice President Nuclear Engineering

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ADQCK

Attachment:

LBLOCA Assessment For St. Lucie Unit PDR 1

QG( i cc: Stewart D. Ebneter, Regional Administrator, Region II, USNRC.

Senior Resident Inspector, USNRC, St. Lucie Plant.

an FPL Group company

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ATTACHMENT LBLOCA Assessment For St. Lucle Unit 1 FPL has performed an assessment for St. Lucie Unit 1 in light of NRC's concern with the calculation of peak cladding temperature (PCT) resulting from a Large Break Loss of Coolant Accident (Reference 1). The NRC identified non-physical behavior in the heat transfer coefficient for reflood rates between 1.00 in/sec and 1.77 in/sec in the NRC approved 1986 ECCS/LBLOCA evaluation model for Siemens Power Corporation (SPC). FPL has developed a modification to the heat transfer coefficient with a linear function between 1.00 in/sec and 1.77 in/sec which corrects the non-physical behavior of the reflood heat transfer correlation. FPL concludes that this modification is appropriate because:

i) The end points for interpolating the heat transfer coefficient are the respective values at flooding rates of 1.00 in/sec and 1.77 in/sec.

ii) The linear interpolation of the heat transfer coefficient between the flooding rates of 1.00 in/sec and 1.77 in/sec follows the trend of increasing heat transfer coefficient with increasing reflood rate shown by the FLECHT test data (Reference 2).

iii) The values of the heat transfer coefficient throughout the range of interest are conservative for pressurized water reactor applications.

An assessment of PCT using the above interpolation approach has shown a PCT of 2027 F (Reference 3), which is an increase of 115 F with respect to the current analysis of record PCT of 1912 F. The recalculated PCT remains well below the 10 CFR 50.46 criterion of 2200 F (margin ) 150 F).

However, the magnitude of the increase meets the definition of significant change per 10 CFR 50.46.

In addition, the preliminary results of the calculation show that the maximum local cladding oxidation is much less than 17% and the core wide maximum oxidation is much less than 1%. In conclusion, the 10 CFR 50.46 acceptance criteria remain satisfied.

The information used by FPL to reach its conclusion is based upon computer code calculations which have not received a formal verification under SPC's and FPL's quality assurance programs. A formal review of this analysis is currently in progress.

Meanwhile, FPL has performed a review of the above analytical results with respect to the following major parameters. The review concludes that the operation of St. Lucie Unit 1 will continue to remain in compliance with 10 CFR 50.46:

Heat Transfer Coefficient: The heat transfer coefficient in the current analysis is less than that seen with the uncorrected 1986 model correlation. The behavior of the heat transfer coefficient with time at various elevations is as expected.

Flooding Rate: The flooding rate shows a drop from a value of -2 in/sec at 75 seconds to a value of -1.2 in/sec at 150 seconds into the transient. The calculated increase in PCT is consistent with the reduced heat transfer coefficient in this range of flooding rates.

l 1-Peak Cladding Temperature: The PCT has increased and the corresponding time to reach the PCT has increased by more than 30 seconds under the reduced heat transfer coefficient assumption. This behavior of PCT following modification of the heat transfer coefficient is as expected and the magnitude of the change appears reasonable.

References:

1. Letter B. W. Sheron (NRR) 'to T. F. Plunkett (FPL),"10 CFR 50.46 Large Break Loss-Of-Coolant Accident Evaluation Model For St. Lucie Unit 1 (TAC No. M96355)," dated October 11, 1996.

2. N. Lee, "PWR FLECHT SEASET Unblocked Bundle, Forced and Gravity Reflood Task, Data Evaluation and Analysis Report," EPRI-NP-2013 NUREG/CR-2256 WCAP-9891 February 1982.

3. Letter TMH:96:223, T. M. Howe (SPC) to R. J. Rodriguez (FPL), "Assessment of Non-Physical Behavior in Heat Transfer for St. Lucie Unit 1 LBLOCA," October 23,1996.

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